Carbon nanotube is a novel material that is garnering attention in quite a number of fields due to its excellent properties, e.g., electroconductivity, thermal conduction, mechanical strength, and so forth. Carbon nanotube is generally synthesized (produced) by placing carbon or a carbon source material under high temperature conditions, possibly in the presence of a catalyst. Examples of typical methods for producing carbon nanotube are the arc discharge procedure, laser ablation technique, and chemical vapor deposition process (CVD processes).
The arc discharge procedure is excellent for obtaining low-defect, high-quality carbon nanotube. However, the arc discharge procedure has a lower carbon nanotube yield than the CVD process. To address this, various methods capable of mass production have been introduced. For example, the method disclosed in Patent Document 1 provides an improved carbon nanotube content in the carbon nanotube-containing product; this is achieved by the incorporation of an iron catalyst in the electrode used. A method of producing carbon nanotube using an electrode that incorporates a nickel-yttrium catalyst is described in Non-Patent Document 1. Carbon nanotube can be obtained in higher yields due to the high activity of the nickel-yttrium catalyst.    Patent Document 1: Japanese Patent Application Laid-open No. 2003-277032    Patent Document 2: Japanese Patent Application Laid-open No. 2002-265209    Patent Document 3: Japanese Patent Application Laid-open No. 2003-89510    Non-Patent Document 1: Yoshinori ANDO et al., Journal of the Society of Materials Science, Japan [Zairyo (Material)], Volume 50, Number 4, pp. 357-360 (April, 2001)
However, the carbon nanotube (product) obtained by each of these methods is admixed with impurities such as the catalyst metal and/or a carbon component other than the carbon nanotube (i.e., a carbon component that is not part of the carbon nanotube), e.g., amorphous carbon. This has made it necessary to purify the obtained carbon nanotube in those instances where a higher purity carbon nanotube is desired.